1. Field of the Invention
The present invention relates generally to the field of liquid chromatography. More particularly, the present invention relates to high throughput systems and methods for the fabrication and measurement of solid oxide fuel cell components using a modified liquid chromatography instrument.
2. Description of the Related Art
A fuel cell is an energy conversion device capable of generating electricity and heat by electrochemically combining a gaseous fuel and an oxidizing gas via an ion-conducting electrolyte. The defining characteristic of a fuel cell is the ability to convert chemical energy directly into electrical energy without the need for combustion, giving much higher conversion efficiencies as compared to conventional methods. A fuel cell is mainly composed of an electrolyte and two electrodes, the anode and the cathode. The classification of fuel cells is generally done according to the nature of the electrolyte.
The electrolyte is operable for preventing the two electrodes from coming into electronic contact while allowing a flow of charged ions generated at the cathode to pass through it in order to be discharged at the anode. The nature of the electrolyte determines the operating temperature of the fuel cell. The function of the electrode is to bring about a reaction between the reactant (fuel) and the electrolyte, without itself being consumed or corroded. It must also, by definition, be an electronic conductor and bring the phases into contact.
There are many different types of fuel cells, and several parameters may vary depending on what the fuel cell is used for. For example, solid oxide fuel cells (SOFCs) are fuel cells constructed entirely from solid-state materials. SOFCs use an ion-conducting oxide ceramic as the electrolyte, and are operated in the range of about 900xc2x0 C. to about 1000xc2x0 C. SOFCs provide several advantages compared to other fuel cell types, such as generating few problems with electrolyte management and having the highest efficiencies of all fuel cells (approximately 50-60%). SOFCs may be used in large-scale power generation, distributed power and vehicular applications.
One of the key challenges in developing a SOFC is developing high-performance electrode and electrolyte materials that meet SOFC performance and cost requirements. While there are lists of potential candidate materials for both electrodes and electrolytes, significant efforts are required to optimize material combinations, chemical compositions, processing conditions and the like. This is especially true as the vast majority of such potential candidate materials are either ternary or quaternary-based.
For example, yttrium-stabilized zirconium (YSZ) is commonly used as an electrolyte material in SOFCs. However, electrolyte performance is relatively sensitive to the ratio of Y to Zr, and this component ratio must be carefully optimized. The same is true for other potential candidate materials for electrolytes, including Sr-doped CeO2, CGO, and the like. Electrode material composition is also critical to the performance of a SOFC. For example, the composition of LaxSrl-xMnO (3-d) (LSM), a common cathode material, may greatly affect its electrical conductivity and electrochemical activity.
Typically, various combinations of elements or components with varying chemical compositions are individually formulated and tested in order to achieve optimal performance for electrode and electrolyte materials, a relatively slow, labor-intensive, and costly process. Thus, what are needed are high-throughput systems and methods that make SOFC-related material development more efficient. The systems and methods of the present invention use a combinatorial or small-scale approach to achieve the high-throughput fabrication, evaluation and optimization of electrode and electrolyte materials for use in SOFCs.
Likewise, although SOFCs are a promising technology for producing electrical energy from fuel with relatively high efficiency and low emissions, barriers to the widespread commercial use of SOFCs include their relatively high manufacturing cost and high operating temperatures. The manufacturing cost is driven primarily by the need for state of the art, electrolyte-supported fuel cells capable of operating at relatively high temperatures (approximately 1000xc2x0 C.). Manufacturing costs may be substantially reduced if the operating temperature could be lowered to below 800xc2x0 C., allowing the use of less expensive structural components, such as stainless steel. A lower operating temperature would also ensure a greater overall system efficiency and a reduction in the thermal stresses in the active ceramic structures, leading to longer life expectancies.
One of the barriers to a reduction in the operating temperature of SOFCs is the efficiency of the common cathode material, LSM. At intermediate temperatures, the cathodic polarization of LSM is relatively high, leading to large efficiency losses. Thus, new cathode compositions with lower activation polarizations are needed. However, standard ceramic processing techniques for fabricating new cathode compositions are time consuming and costly. Typically, new powder compositions are synthesized in a plurality of steps, including precipitation, filtration, and calcining. Because the microstructure (i.e., the porosity) of the cathode structure contributes substantially to its performance, careful processing of the powder must be performed in order to produce cathode structures with uniform microstructures. The expense associated with synthesizing such ceramic powders limits the number of cathode compositions that may be fabricated and evaluated.
Thus, what is needed are high-throughput systems and methods for the fabrication and evaluation of electrolyte and electrode material performance for solid oxide fuel cells. Further, what is needed are systems and methods to synthesize and optimize the performance of electrode and electrolyte combinations. Still further, what is needed are small scale techniques to optimize these materials based on chemical composition and variable processing. Rapid device performance methods coupled with structural and surface methods would allow for an increased discovery rate of new materials for SOFCs.
In various embodiments, the present invention provides high-throughput systems and methods for the fabrication and evaluation of electrode and electrolyte materials for use in solid oxide fuel cells (xe2x80x9cSOFCsxe2x80x9d). The present invention comprises systems and methods for synthesizing, evaluating, and optimizing the performance of such electrodes and electrode-electrolyte combinations and uses small-scale techniques to perform such synthesis, evaluation and optimization based on variable chemical composition and processing. Advantageously, rapid device performance systems and methods coupled with structural and surface systems and methods allow for increased rates of discovery for new materials and material combinations for use in SOFCs.
In various embodiments, the present invention provides facile and rapid techniques for synthesizing multi-compositional inorganic materials generally. These techniques may be used to discover new inorganic materials for use in SOFCs (such as electrodes, electrolytes, interconnects, seals, and the like), phosphors, scintillators, PZT materials, and the like. The techniques allow for the synthesis and analysis of gradient or spatially resolved compositions that may be used to offset non-steady-state applications.
In one embodiment of the present invention, a method for the fabrication and evaluation of an array of electrode or electrolyte materials for use in SOFCs comprises providing a plurality of materials suitable for delivery to the surface of a substrate. As described above, the plurality of materials may form a gradient coating in the form of a gradient array on the surface of the substrate or, alternatively, they may infiltrate the substrate, forming an array of electrode or electrolyte materials suitable for evaluation. The plurality of materials may form the array of electrode or electrolyte materials by selectively altering the chemical composition and/or physical microstructure of each of a plurality of regions of the substrate.
In another embodiment, for example, a plurality of components are mixed in tubes of a liquid chromatography (LC) instrument. Any number of components may be added and a gradient flow of the components may be accomplished using LC software. In yet another embodiment, the gradient flow is formed as previously described, but after the various components are delivered to the substrate 106, a processing step is carried out which allows or causes the components to interact to form layers, blends, mixtures, and/or materials resulting from a reaction between components. In a further embodiment, two or more components may be delivered to predefined regions on the substrate using a parallel delivery technique, such that the components interact with each other before contacting the substrate 106. Each component may be delivered in either a uniform or gradient fashion to produce either a single stoichiometry or, alternatively, a large number of stoichiometries within a single predefined region.
With the synthesis of materials for SOFCs, both chemical composition and microstructure are important variables. Producing a gradient flow using the methods and systems of the present invention promotes the replication of compositional libraries, thus opportunities for processing with multiple variables and microstructure control are feasible. Replication of the arrays allows for the investigation of multi-processing variables. The individual compositions in a given array may be tested for conductivity and for catalytic activity in the presence of oxygen by monitoring the overpotential at various temperatures using a multi-probe instrument. Subsequent results allow for the ranking of composition and processing based on performance measurements.
In a still further embodiment, the present invention provides a system for the fabrication and evaluation of a gradient mixture of solid oxide fuel cell components. The system comprises a substrate, a liquid chromatography instrument operable for simultaneously and continuously controlling 2 or more solution flow rates, an injection system operable for serially and distributively injecting samples selected from a sample library into the gradient mixture to form a multi-compositional material, and a delivery device operable for delivering the gradient mixture to the substrate.
In a still further embodiment, the system further comprises an x-y motion stage connected to the delivery device, the substrate or both, wherein motion of the x-y stage is coordinated with the delivery of the gradient mixture to the substrate, a mask operable for creating discrete or continuous gradient compositions, a shutter operable for selectively allowing/preventing the mixture from being sprayed onto the substrate by opening/closing, and a general purpose processor operable for controlling functions of at least one of the following: the liquid chromatography instrument, the injection system, the delivery device, the x-y motion stage, the mask, the shutter, and the temperature controlled heating block.
In a still further embodiment, the present invention provides a system comprising a substrate, an auto-sampler operable for simultaneously controlling the flow rates of 2 or more solid oxide fuel cell components, and wherein the auto-sampler is further operable for serially and distributively injecting samples selected from a sample library into a gradient mixture to form a multi-compositional material, a delivery apparatus operable for delivery the gradient mixture to the substrate, a mass flow controller operable for controlling the flow of the gradient mixture to the substrate, an x-y motion stage attached to either the substrate of the delivery apparatus, an a microprocessor for controlling the function of the auto-sampler, the delivery apparatus, the mass flow controller and the x-y motion stage.
In a still further embodiment, the present invention provides a method for the fabrication and evaluation of electrode and electrolyte material performance for solid oxide fuel cells. The method comprises providing a library of samples comprising electrode materials, electrolyte materials, metals, non-metals, soluble metal salts, organic binders, polymers, and any other components used to produce the solid oxide fuel cells, continuously and controllably supplying desired amounts of the samples to a liquid chromatography system where a multi-compositional mixture is formed, serially loading the multi-compositional mixture into a common sprayer, serially and distributively spraying the multi-compositional mixture onto a surface of a substrate using a spraying apparatus, forming a discrete or continuous gradient array of the mixture reacted on the substrate, and evaluating the performance of the mixture for use in solid oxide fuel cells.